"We should be able to do 90% of miles driven within three years," said Musk. Tesla's self-driven cars will not be fully autonomous, however, so any notion of hopping in the back for a quick 40 winks should be dispensed with—meaning that the Tesla concept sounds more like a very sophisticated version of cruise control.

Until recently, it was thought that Google would be the first firm to bring the robot to the driving seat. It showed off the initial technology three years ago but little has been heard. With Musk calling his version "auto-pilot," it's probably safe to say that Google's concept is the more sophisticated one, and therefore will probably be harder to get right.